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Configuring device mapper multipath

Red Hat Enterprise Linux 10

Configuring and managing the Device Mapper Multipath feature

Red Hat Customer Content Services

Abstract

With Device mapper multipathing (DM Multipath), you can configure multiple I/O paths between server nodes and storage arrays into a single device. These I/O paths are physical Storage Area Network (SAN) connections that can include separate cables, switches, and controllers.
Multipathing aggregates the I/O paths and creates a new device that consists of the aggregated paths.

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Chapter 1. Overview of device mapper multipathing
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DM Multipath provides redundancy through failover in active/passive configurations and improved performance by spreading I/O across multiple paths in active/active mode.

DM Multipath provides:

Redundancy

DM Multipath can provide failover in an active/passive configuration. In an active/passive configuration, only a subset of the paths is used at any time for I/O. If any element of an I/O path such as the cable, switch, or controller fails, DM Multipath switches to an alternate path. For more information, see:

  • multipath(8) and multipathd(8) man pages on your system
  • /etc/multipath.conf file
Note

The number of paths is dependent on the setup. Usually, DM Multipath setups have 2, 4, or 8 paths to the storage, but this is a common setup and other numbers are possible for the paths.

Improved Performance
DM Multipath can be configured in an active/active mode, where I/O is spread over the paths in a round-robin fashion. In some configurations, DM Multipath can detect loading on the I/O paths and dynamically rebalance the load.

1.1. Active/Passive multipath configuration with one RAID device
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Active/passive configuration provides redundant I/O paths through dual HBAs and SAN switches to a single RAID device, enabling automatic failover when path components fail.

In this configuration, there are two Host Bus Adapters (HBAs) on the server, two SAN switches, and two RAID controllers. Following are the possible failure in this configuration:

  • HBA failure
  • Fibre Channel cable failure
  • SAN switch failure
  • Array controller port failure

With DM Multipath configured, a failure at any of these points causes DM Multipath to switch to the alternate I/O path. The following image describes the configuration with two I/O paths from the server to a RAID device. Here, there is one I/O path that goes through hba1, SAN1, and cntrlr1 and a second I/O path that goes through hba2, SAN2, and cntrlr2.

Figure 1.1. Active/Passive multipath configuration with one RAID device

Active/Passive multipath configuration with one RAID device
View larger image
Active/Passive multipath configuration with one RAID device

1.2. Active/Passive multipath configuration with two RAID devices
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Active/passive configuration with dual RAID devices provides redundant paths to multiple storage arrays, ensuring failover protection across separate RAID systems with dedicated controllers.

In this configuration, there are two HBAs on the server, two SAN switches, and two RAID devices with two RAID controllers each. With DM Multipath configured, a failure at any of the points of the I/O path to either of the RAID devices causes DM Multipath to switch to the alternate I/O path for that device. The following image describes the configuration with two I/O paths to each RAID device. Here, there are two I/O paths to each RAID device.

Figure 1.2. Active/Passive multipath configuration with two RAID device

Active/Passive multipath configuration with two RAID device
View larger image
Active/Passive multipath configuration with two RAID device

1.3. Active/Active multipath configuration with one RAID device
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Active/active configuration enables simultaneous I/O across multiple paths to a RAID device, distributing workload for improved performance while maintaining failover capability.

In this configuration, there are two HBAs on the server, two SAN switches, and two RAID controllers. The following image describes the configuration with two I/O paths from the server to a storage device. Here, I/O can be spread among these two paths.

Figure 1.3. Active/Active multipath configuration with one RAID device

Active/Active multipath configuration with one RAID device
View larger image
Active/Active multipath configuration with one RAID device

1.4. DM Multipath components
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DM Multipath consists of kernel modules, utilities, and daemons that work together to manage multiple I/O paths, including the multipathd daemon and multipath command tools.

The following table describes the DM Multipath components.

Expand
Table 1.1. Components of DM Multipath

Component

Description

dm_multipath kernel module

Reroutes I/O and supports failover for paths and path groups.

mpathconf utility

Configures and enables device mapper multipathing.

multipath command

Lists and configures the multipath devices. It is also executed by udev whenever a block device is added, to determine if the device should be part of a multipath device or not.

multipathd daemon

Automatically creates and removes multipath devices and monitors paths; as paths fail and come back, it may update the multipath device. Allows interactive changes to multipath devices. Reload the service if there are any changes to the /etc/multipath.conf file.

kpartx command

Creates device mapper devices for the partitions on a device. This command is automatically executed by udev when multipath devices are created to create partition devices on top of them. The kpartx command is provided in its own package, but the device-mapper-multipath package depends on it.

mpathpersist

Sets up SCSI-3 persistent reservations on multipath devices. This command works similarly to the way sg_persist works for SCSI devices that are not multipathed, but it handles setting persistent reservations on all paths of a multipath device. It coordinates with multipathd to ensure that the reservations are set up correctly on paths that are added later. To use this functionality, the reservation_key attribute must be defined in the /etc/multipath.conf file. Otherwise the multipathd daemon will not check for persistent reservations for newly discovered paths or reinstated paths.

1.5. Displaying multipath topology
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To effectively monitor paths, troubleshoot multipath issues, or check whether the multipath configurations are set correctly, you can display the multipath topology.

Procedure

  1. Display the multipath device topology: 

    # multipath -ll
mpatha (3600d0230000000000e13954ed5f89300) dm-4 WINSYS,SF2372
size=233G features='1 queue_if_no_path' hwhandler='0' wp=rw
`-+- policy='service-time 0' prio=1 status=active
  `- 6:0:0:0 sdf 8:80 active ready running
    Copy to Clipboard Toggle word wrap

    The output can be split into three parts. Each part displays information for the following group:

    • Multipath device information:

      • mpatha (3600d0230000000000e13954ed5f89300): alias (wwid if it’s different from the alias)
      • dm-4: dm device name
      • WINSYS,SF2372: vendor, product
      • size=233G: size
      • features='1 queue_if_no_path': features
      • hwhandler='0': hardware handler
      • wp=rw: write permissions

    • Path group information:

      • policy='service-time 0': scheduling policy
      • prio=1: path group priority
      • status=active: path group status

    • Path information:

      • 6:0:0:0: host:channel:id:lun
      • sdf: devnode
      • 8:80: major:minor numbers
      • active: dm status
      • ready: path status

      • running: online status

        For more information about the dm, path and online status, see Path status.

        Other multipath commands, which are used to list, create, or reload multipath devices, also display the device topology. However, some information might be unknown and shown as undef in the output. This is normal behavior. Use the multipath -ll command to view the correct state.

        Note

        In certain cases, such as creating a multipath device, the multipath topology displays a parameter, which represents if any action was taken. For example, the following command output shows the create: parameter to represent that a multipath device was created: 

        create: mpatha (3600d0230000000000e13954ed5f89300) undef WINSYS,SF2372
size=233G features='1 queue_if_no_path' hwhandler='0' wp=undef
`-+- policy='service-time 0' prio=1 status=undef
  `- 6:0:0:0 sdf 8:80 undef ready running
        Copy to Clipboard Toggle word wrap

1.6. Path status
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Path status indicates the current state of individual storage paths, ranging from ready and functional to faulty or delayed, helping determine multipath device health and behavior.

The path status is updated periodically by the multipathd daemon based on the polling interval defined in the /etc/multipath.conf file. In terms of the kernel, the dm status is similar to the path status. The dm state will retain its current status until the path checker has completed.

Path status
ready, ghost
The path is up and ready for I/O.
faulty, shaky
The path is down.
i/o pending
The checker is actively checking this path, and the state will be updated shortly.
i/o timeout
The checker did not return success/failure before the timeout period. This is treated the same as faulty.
removed
The path has been removed from the system, and will shortly be removed from the multipath device. This is treated the same as faulty.
wild
multipathd was unable to run the path checker, because of an internal error or configuration issue. This is treated the same as faulty, except multipath will skip many actions on the path.
unchecked
The path checker has not run on this path, either because it has just been discovered, it does not have an assigned path checker, or the path checker encountered an error. This is treated the same as wild.
delayed
The path checker returns that the path is up, but multipath is delaying the reinstatement of the path because the path has recently failed multiple times and multipath has been configured to delay paths in this case. This is treated the same as faulty.
Dm status
Active
Maps to the ready and ghost path status.
Failed
Maps to all other path status, except i/o pending that does not have an equivalent dm state.
Online status
Running
The device is enabled.
Offline
The device has been disabled.

Chapter 2. Multipath devices
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DM Multipath creates a single multipath device over multiple I/O paths to the same storage, organizing them logically. Without it, each path is seen as a separate device, even if they connect the same server to the same storage controller.

2.1. Multipath device identifiers
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Multipath devices use specific naming conventions that determine how they appear in the file system. They can be identified by their World Wide Identifier (WWID) or user-friendly names like mpathN, depending on your configuration preferences.

When new devices are under the control of DM Multipath, these devices are created in the /dev/mapper/ and /dev/ directory.

Note

Any devices of the form /dev/dm-X are for internal use only and should never be used by the administrator directly.

The following describes multipath device names:

  • When the user_friendly_names configuration option is set to no, the name of the multipath device is set to World Wide Identifier (WWID). By default, the name of a multipath device is set to its WWID. The device name would be /dev/mapper/WWID. It is also created in the /dev/ directory, named as /dev/dm-X.
  • Alternately, you can set the user_friendly_names option to yes in the /etc/multipath.conf file. This sets the alias in the multipath section to a node-unique name of the form mpathN. The device name would be /dev/mapper/mpathN and /dev/dm-X. But the device name is not guaranteed to be the same on all nodes using the multipath device. Similarly, if you set the alias option in the /etc/multipath.conf file, the name is not automatically consistent across all nodes in the cluster.
Note

This should not cause any difficulties if you use LVM to create logical devices from the multipath device. To keep your multipath device names consistent in every node, disable the user_friendly_names option.

For example, a node with two HBAs attached to a storage controller with two ports by means of a single unzoned FC switch sees four devices: /dev/sda, /dev/sdb, /dev/sdc, and /dev/sdd. DM Multipath creates a single device with a unique WWID that reroutes I/O to those four underlying devices according to the multipath configuration.

In addition to the user_friendly_names and alias options, a multipath device also has other attributes. You can modify these attributes for a specific multipath device by creating an entry for that device in the multipaths section of the /etc/multipath.conf file. For more information, see:

  • multipath(8) and multipath.conf(8) man pages on your system
  • /etc/multipath.conf file

2.2. Multipath devices in logical volumes
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Multipath devices integrate seamlessly with LVM, allowing you to create physical volumes, volume groups, and logical volumes by using multipath device names instead of individual disk paths.

After creating multipath devices, you can use the multipath device names as you would use a physical device name when creating an Logical volume manager (LVM) physical volume. For example, if /dev/mapper/mpatha is the name of a multipath device, the pvcreate /dev/mapper/mpatha command marks /dev/mapper/mpatha as a physical volume.

You can use the resulting LVM physical device when you create an LVM volume group just as you would use any other LVM physical device.

To filter all the sd devices in the /etc/lvm/lvm.conf file, add the filter = [ "r/block/", "r/disk/", "r/sd./", "a/./" ] filter in the devices section of the file. For more information see the lvm.conf man page on your system.

Note

If you attempt to create an LVM physical volume on a whole device on which you have configured partitions, the pvcreate command fails. The Anaconda and Kickstart installation programs create empty partition tables if you do not specify otherwise for every block device. If you want to use the whole device instead of creating a partition, remove the existing partitions from the device. You can remove existing partitions with the kpartx -d device command and the fdisk utility. If your system has block devices that are greater than 2Tb, use the parted utility to remove partitions.

When you create an LVM logical volume that uses active/passive multipath arrays as the underlying physical devices, you can optionally include filters in the /etc/lvm/lvm.conf file to exclude the disks that underline the multipath devices. This is because if the array automatically changes the active path to the passive path when it receives I/O, multipath will failover and failback whenever LVM scans the passive path, if these devices are not filtered.

The kernel changes the active/passive state by automatically detecting the correct hardware handler to use. For active/passive paths that require intervention to change their state, multipath automatically uses this hardware handler to do so as necessary. If the kernel does not automatically detect the correct hardware handler to use, you can configure which hardware handler to use in the multipath.conf file with the "hardware_handler" option. For active/passive arrays that require a command to make the passive path active, LVM prints a warning message when this occurs.

Depending on your configuration, LVM may print any of the following messages:

  • LUN not ready: 

    end_request: I/O error, dev sdc, sector 0
sd 0:0:0:3: Device not ready: <6>: Current: sense key: Not Ready
    Add. Sense: Logical unit not ready, manual intervention required
    Copy to Clipboard Toggle word wrap

  • Read failed: 

    /dev/sde: read failed after 0 of 4096 at 0: Input/output error
    Copy to Clipboard Toggle word wrap

The following are the reasons for the mentioned errors:

  • Multipath is not set up on storage devices that are providing active/passive paths to a machine.
  • Paths are accessed directly, instead of through the multipath device.

Chapter 3. Configuring DM Multipath
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Configure DM Multipath using the mpathconf utility, which creates or edits the /etc/multipath.conf configuration file to set up basic failover and additional storage options.

This utility creates or edits the /etc/multipath.conf multipath configuration file based on the following scenarios:

  • If the /etc/multipath.conf file already exists, the mpathconf utility will edit it.
  • If the /etc/multipath.conf file does not exist, the mpathconf utility will create the /etc/multipath.conf file from scratch.

3.1. Checking for the device-mapper-multipath package
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Verify that the device-mapper-multipath package is installed on your system to ensure all necessary components are available before configuring multipathing. This prevents potential failures caused by missing core software.

Procedure

  1. Check if your system includes the device-mapper-multipath package: 

    # rpm -q device-mapper-multipath
device-mapper-multipath-current-package-version
    Copy to Clipboard Toggle word wrap

    If your system does not include the package, it prints the following: 

    package device-mapper-multipath is not installed
    Copy to Clipboard Toggle word wrap

  2. If your system does not include the package, install it by running the following command: 

    # dnf install device-mapper-multipath
    Copy to Clipboard Toggle word wrap

3.2. Setting up basic failover configuration with DM Multipath
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Establishing a basic failover configuration for DM Multipath provides path redundancy and enhances storage reliability. It ensures that I/O operations continue through alternate paths if one fails, preventing downtime or data loss.

Prerequisites

  • Administrative access.

Procedure

  1. Enable and initialize the multipath configuration file: 

    # mpathconf --enable
    Copy to Clipboard Toggle word wrap

  2. Optional: Edit the /etc/multipath.conf file.

    Most default settings are already configured, including path_grouping_policy which is set to failover.

  3. Optional: The default naming format of multipath devices is set to /dev/mapper/mpathn format. If you prefer a different naming format:

    1. Configure DM Multipath to use the multipath device WWID as its name, instead of the mpath_n_ user-friendly naming scheme: 

      # mpathconf --enable --user_friendly_names n
      Copy to Clipboard Toggle word wrap

    2. Reload the configuration of the DM Multipath daemon: 

      # systemctl reload multipathd.service
      Copy to Clipboard Toggle word wrap

  4. Start the DM Multipath daemon: 

    # systemctl start multipathd.service
    Copy to Clipboard Toggle word wrap

Verification

  • Confirm that the DM Multipath daemon is running without issues: 

    # systemctl status multipathd.service
    Copy to Clipboard Toggle word wrap

  • Verify the naming format of multipath devices: 

    # ls /dev/mapper/
    Copy to Clipboard Toggle word wrap

3.3. Ignoring local disks when generating multipath devices
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To prevent DM Multipath from using local SCSI disks, you can configure it to ignore these devices during multipath device generation. Setting find_multipaths to on simplifies this process; otherwise, manual exclusion is required in the configuration file.

Procedure

  1. Identify the internal disk using any known parameters such as the device’s model, path or vendor, and determine its WWID by using any one of the following options:

    • Display existing multipath devices: 

      # multipath -v2 -l

mpatha (WDC_WD800JD-75MSA3_WD-WMAM9FU71040) dm-2 ATA,WDC WD800JD-75MS
size=33 GB features="0" hwhandler="0" wp=rw
`-+- policy='round-robin 0' prio=0 status=active
  |- 0:0:0:0 sda 8:0 active undef running
      Copy to Clipboard Toggle word wrap

    • Display additional multipath devices that DM Multipath could create: 

      # multipath -v2 -d

: mpatha (WDC_WD800JD-75MSA3_WD-WMAM9FU71040) dm-2 ATA,WDC WD800JD-75MS
size=33 GB features="0" hwhandler="0" wp=undef
`-+- policy='round-robin 0' prio=1 status=undef
  |- 0:0:0:0 sda 8:0  undef ready running
      Copy to Clipboard Toggle word wrap

    • Display device information: 

      # multipathd show paths raw format "%d %w" | grep sda
sda WDC_WD800JD-75MSA3_WD-WMAM9FU71040
      Copy to Clipboard Toggle word wrap

      In this example, /dev/sda is the internal disk and its WWID is WDC_WD800JD-75MSA3_WD-WMAM9FU71040.

  2. Edit the blacklist section of the /etc/multipath.conf file to ignore this device, using its WWID attribute: 

    blacklist {
      wwid WDC_WD800JD-75MSA3_WD-WMAM9FU71040
}
    Copy to Clipboard Toggle word wrap
    Warning

    Although you could identify the device using its devnode parameter, such as sda, it would not be a safe procedure, because /dev/sda is not guaranteed to refer to the same device on reboot.

  3. Check for any configuration errors in the /etc/multipath.conf file: 

    # multipath -t > /dev/null
    Copy to Clipboard Toggle word wrap

    To see the full report, do not discard the command output: 

    # multipath -t
    Copy to Clipboard Toggle word wrap
  4. Remake the initramfs if the disk is included in initramfs. For more information, see Configuring multipathing in initramfs.

  5. Reload the /etc/multipath.conf file by reconfiguring the multipathd daemon: 

    # systemctl reload multipathd
    Copy to Clipboard Toggle word wrap
    Note

    Multipath devices on top of local disks cannot be removed when in use. To ignore such device, stop all users of the device. For example, by unmounting any filesystem on top of it and deactivating any logical volumes using it. If this is not possible, you can reboot the system to remove the multipath device.

Verification

  1. Verify that the internal disk is ignored and it is not displayed in the multipath output:

    • List the multipathed devices: 

      # multipath -v2 -l
      Copy to Clipboard Toggle word wrap

    • List the additional devices that DM Multipath could create: 

      # multipath -v2 -d
      Copy to Clipboard Toggle word wrap

3.4. Configuring additional storage with DM Multipath
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By default, DM Multipath includes built-in configurations for the most common storage arrays, which support DM Multipath. If your storage array does not already have a configuration, you can add one by editing the /etc/multipath.conf file.

Note

Add additional storage devices during the initial configuration to align the setup with your anticipated needs. DM Multipath enables adding devices later for scalability or upgrades, but this approach may require adjusting configurations to ensure compatibility.

Procedure

  1. View the default configuration value and supported devices: 

    # multipathd show config
    Copy to Clipboard Toggle word wrap

  2. Edit the /etc/multipath.conf file to set up your multipath configuration. Below is an example for the DM Multipath configuration for HP OPEN-V Storage Device: 

    # Set default configurations for all devices managed by DM Multipath

defaults {
    # Enable user-friendly names for devices
    user_friendly_names yes
}

devices {
    # Define configuration for HP OPEN-V storage
    device {
        vendor "HP"
        pproduct "OPEN-V"
        no_path_retry 18
    }
}
    Copy to Clipboard Toggle word wrap
  3. Save your changes and close the editor.

  4. Update the multipath device list by scanning for new devices: 

    # multipath -r
    Copy to Clipboard Toggle word wrap

Verification

  • Confirm that the multipath devices are recognized correctly: 

    # multipath -ll
    Copy to Clipboard Toggle word wrap

3.5. Configuring multipathing in initramfs
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Setting up multipathing in the initramfs ensure multipath devices are available early in the boot process. This is essential for storage setups requiring redundancy and load balancing, helping maintain system integrity and avoid issues during startup.

Prerequisites

  • Configured DM multipath on your system.

Procedure

  1. Rebuild the initramfs file system with the multipath configuration files: 

    # dracut --force --add multipath
    Copy to Clipboard Toggle word wrap
    Note

    When using multipath in the initramfs and modifying its configuration files, remember to rebuild the initramfs for the changes to take effect. If your root device employs multipath, the dracut command will automatically include the multipath module in the initramfs.

  2. Optional: If multipath in the initramfs is no longer necessary:

    1. Remove the multipath configuration file: 

      # rm /etc/dracut.conf.d/multipath.conf
      Copy to Clipboard Toggle word wrap

    2. Rebuild the initramfs with the added multipath configuration: 

      # dracut --force --omit multipath
      Copy to Clipboard Toggle word wrap

Verification

  • Check if multipath-related files and configurations are present: 

    # lsinitrd /path/to/initramfs.img -m | grep multipath
    Copy to Clipboard Toggle word wrap
Note

While verification steps provided can give you an indication of success, a final test boot-up is recommended to ensure that the configuration works as expected.

  • After the reboot, confirm that the multipath devices are recognized correctly: 

    # multipath -ll
    Copy to Clipboard Toggle word wrap

Chapter 4. Modifying the DM Multipath configuration file
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Override DM Multipath default configuration values by editing the /etc/multipath.conf file to customize multipathing behavior and add support for unsupported storage arrays.

In the multipath configuration file, you need to specify only the sections that you need for your configuration, or that you need to change from the default values. If there are sections of the file that are not relevant to your environment or for which you do not need to override the default values, you can leave them commented out, as they are in the initial file.

In the configuration file, you can also use the regular expression.

Note

If you run multipath from the initramfs file system and you make any changes to the multipath configuration files, you must rebuild the initramfs file system for the changes to take effect.

4.1. Configuration file overview
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The multipath configuration file contains distinct sections for blacklists, defaults, devices, multipaths, and overrides, evaluated in priority order to determine device behavior.

The multipath configuration file is divided into the following sections:

blacklist
Listing of specific devices that will not be considered for multipath.
blacklist_exceptions
Listing of multipath devices that would otherwise be ignored according to the parameters of the blacklist section.
defaults
General default settings for DM Multipath.
multipaths
Settings for the characteristics of individual multipath devices. These values overwrite what is specified in the overrides, devices, and defaults sections of the configuration file.
devices
Settings for the individual storage controllers. These values overwrite what is specified in the defaults section of the configuration file. If you are using a storage array that is not supported by default, you may need to create a devices subsection for your array.
overrides
Settings that are applied to all devices. These values overwrite what is specified in the devices and defaults sections of the configuration file.

When the system determines the attributes of a multipath device, it checks the settings of the separate sections from the multipath.conf file in the following order:

  1. multipaths section
  2. overrides section
  3. devices section
  4. defaults section

The following are the ways to view the default configurations:

  • If you install your machine on a multipath device, the default multipath configuration applies automatically. The default configuration includes the following:

    • For a complete list of the default configuration values, execute either multipath -t or multipathd show config command.
    • For a list of configuration options with descriptions, see the multipath.conf man page on your system.
  • If you did not set up multipathing during installation, execute the mpathconf --enable command to get the default configuration.

4.2. Configuration file defaults
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The defaults section establishes global configuration parameters for DM Multipath behavior, including polling intervals, path grouping policies, and failover settings applied to all multipath devices.

The /etc/multipath.conf configuration file contains a defaults section. This section includes the default configuration of Device Mapper (DM) Multipath. The default values might differ based on your initial device settings.

The following table describes the optional attributes, set in the defaults section of the multipath.conf configuration file. If you do not set them, default values from the overrides, or devices sections apply.

Expand
Table 4.1. Multipath configuration defaults
AttributeDescription

polling_interval

Specifies the interval between two path checks in seconds. For properly functioning paths, the interval between checks gradually increases to max_polling_interval.

The default value is 5.

max_polling_interval

Specifies the maximum length of the interval between two path checks in seconds.

The default value is 4 * polling_interval.

find_multipaths

Defines the mode for setting up multipath devices. Available values include:

off: If find_multipaths is set to off, multipath applies rules as with the strict value and the multipathd daemon applies rules as with the greedy value.

on: If there are at least two devices that are not on the blacklist with the same World Wide Identifier (WWID), or if multipath created a multipath device with a device WWID before (even if that multipath device is no longer present), then the device is treated as a multipath device path.

greedy: Both multipathd and multipath treat every non-blacklisted device as a multipath device path.

smart: Multipath automatically considers that every non-blacklisted device is a multipath device path. If a second path, with the same WWID does not appear within the time set for find_multipaths_timeout, multipath releases the device and enables it for use by the rest of the system. The multipathd daemon applies rules as with the on value.

strict: This value only treats a device as a multipath path, if you create a multipath device with the device WWID.

The default value is off. The default multipath.conf file sets find_multipaths to on.

find_multipaths_timeout

This represents the timeout in seconds, to wait for additional paths after detecting the first one, if find_multipaths smart is set. Possible values include:

Positive value: If set with a positive value, the timeout applies for all non-blacklisted devices.

Negative value: If set with a negative value, the timeout applies only to known devices that have an entry in the multipath hardware table, either in the built-in table, or in a device section. Other unknown devices use a timeout of only 1 second to avoid booting delays.

0: The system applies the built-in default for this attribute.

The default value for known hardware is -10. This means that known devices have a 10 second timeout. Unknown devices have a 1 second timeout. If the find_multipaths attribute has a value other than smart, this attribute has no effect.

uxsock_timeout

Set the timeout of multipathd interactive commands in milliseconds.

For systems with a large number of devices, multipathd interactive commands might timeout and fail. If this happens, increase this timeout to resolve the issue.

The default value is 4000.

reassign_maps

Enable reassigning of device-mapper maps. With this option, the multipathd daemon remaps existing device-mapper maps to always point to the multipath device, not the underlying block devices. Possible values are yes and no. The default value is no.

verbosity

The default verbosity value is 2. Higher values increase the verbosity level. Valid levels are between 0 and 4.

path_selector

Specifies the default algorithm to use in determining what path to use for the next I/O operation. Possible values include:

round-robin 0: Loop through every path in the path group, sending the same number of I/O requests, determined by rr_min_io or rr_min_io_rq, to each.

queue-length 0: Send the next group of I/O requests down the path with the least number of outstanding I/O requests.

service-time 0: Send the next group of I/O requests down the path with the shortest estimated service time. This is determined by dividing the total size of the outstanding I/O to each path by the relative throughput.

The default value is service-time 0.

path_grouping_policy

Specifies the default path grouping policy to apply to unspecified multipaths. Possible values include:

failover: 1 path per priority group.

multibus: All valid paths in 1 priority group.

group_by_serial: 1 priority group per detected serial number.

group_by_prio: 1 priority group per path priority value. Priorities are determined by the prio attribute.

group_by_node_name: 1 priority group per target node name. The /sys/class/fc_transport/target*/node_name directory includes target node names.

group_by_tpg: 1 priority group per target port group. All paths in the multipath device must have their priority function set to alua or sysfs.

The default value is failover.

uid_attrs

Set this option to activate merging uevents by WWID. This action might improve uevent processing efficiency. It is also an alternative method to configure the udev properties to use for determining unique path identifiers (WWIDs).

The value of this option is a space separated list of records like type:ATTR, where type is matched against the beginning of the device node name, and ATTR is the name of the udev property to use for matching devices.

If you configure this option and it matches the device node name of a device, it overrides any other configured methods for determining the WWID for this device.

You can enable uevent merging by setting this value to sd:ID_SERIAL dasd:ID_UID nvme:ID_WWN.

The default is unset.

prio

Specifies the default function to call to obtain a path priority value. For example, the ALUA bits in SPC-3 provide an exploitable prio value. Possible values include:

const: Set a priority of 1 to all paths.

emc: Generate the path priority for EMC arrays.

sysfs: Generate the path priority from sysfs. This prioritizer accepts the optional prio_arg value exclusive_pref_bit. The sysfs value uses the sysfs attributes access_state and preferred_path.

alua: Generate the path priority based on the SCSI-3 ALUA settings. If you specify prio alua and prio_args exclusive_pref_bit in your device configuration, multipath creates a path group that contains only the path with the exclusive_pref_bit set, and assigns that path group the highest priority. Refer to the multipath.conf(5) man page for more information about this type of cases.

ontap: Generate the path priority for NetApp arrays.

rdac: Generate the path priority for LSI/Engenio RDAC controller.

hp_sw: Generate the path priority for Compaq/HP controller in active/standby mode.

hds: Generate the path priority for Hitachi HDS Modular storage arrays.

random: Generate a random priority between 1 and 10.

weightedpath: Generate the path priority based on the regular expression and the provided priority as an argument. Requires a prio_args keyword.

path_latency: Generate the path priority based on a latency algorithm. Requires a prio_args keyword.

ana: Generate the path priority based on the NVMe ANA settings. This priority routine is hardware dependent.

datacore: Generate the path priority for some DataCore storage arrays. Requires a prio_args keyword. This priority routine is hardware dependent.

iet: Generate path priority for iSCSI targets based on IP their address. Requires a prio_args keyword. This priority routine is available only with iSCSI.

The default value depends on the detect_prio setting. If detect_prio is set to yes, then the default priority algorithm is sysfs. The only exception is for NetAPP E-Series, where the default is alua. If detect_prio is set to no, the default priority algorithm is const.

prio_args

Arguments to pass to the prio function. This applies only to the following prioritizers:

weighted: Needs a value of the form <hbtl,devname,serial,wwn> <regex1> <prio1> <regex2> <prio2>

hbtl: The Regex value can be of SCSI H:B:T:L format. For example: 1:0:.:. , *:0:0:.

devname: The Regex value can be in device name format. For example: sda, sd.e.

serial: The Regex value can be in serial number format. Look up serial through sysfs, or by running the command multipathd show paths format "%z".

wwn: The Regex value can be in the form host_wwnn:host_wwpn:target_wwnn:target_wwpn. These values can be looked up through sysfs or by running the command multipathd show paths format %N:%R:%n:%r".

path_latency: Requires a value in the form io_num= <integer> base_num=<integer>.

io_num: The number of read IOs, continuously sent to the current path. This value helps calculate the average path latency. Valid values include Integer, [2, 200].

base_num: The base number value of logarithmic scale. This value helps to partition different priority ranks. Valid values include Integer, [2, 10]. The maximum average latency value is 100s and the minimum average latency value is 1us.

alua: If the exclusive_pref_bit value is set, paths with the preferred_path_bit set always create their own path group.

sysfs: If the exclusive_pref_bit value is set, paths with the preferred_path_bit set always create their own path group.

datacore: Requires a value of the form timeout=<milliseconds> preferredsds=<name>.

preferredsds: This value is mandatory and it represents the preferred SDS name.

timeout: This value is optional. Set the timeout for the inquiry in milliseconds.

iet: Requires a value of the form preferredip=<ip_address>.

preferredip: This value is mandatory. This is the preferred IP address, in dotted decimal notation, for iSCSI targets.

The default value is unset.

features

The default extra features of multipath devices, using the format: "number_of_features_plus_arguments feature1 …​".

Possible values for features include:

queue_if_no_path: The same as setting no_path_retry to queue.

pg_init_retries n: Retry path group initialization up to n times before failing. The number must be between 1 and 50.

pg_init_delay_msecs msecs: Number of milliseconds before pg_init retry initiates. The number must be between 0 and 60000.

queue_mode mode: Select the queueing mode per multipath device. The mode value options are bio, rq or mq. These correspond to bio-based, request-based, and block-multiqueue request-based (blk-mq), respectively.

By default, the value is unset.

path_checker

Specifies the default method to determine the state of the paths. Possible values include:

readsector0: Read the first sector of the device.

tur: Issue a TEST UNIT READY command to the device.

emc_clariion: Query the EMC Clariion specific EVPD page 0xC0 to determine the path.

hp_sw: Check the path state for HP storage arrays with Active/Standby firmware.

rdac: Check the path state for LSI/Engenio RDAC storage controller.

directio: Read the first sector with direct I/O.

cciss_tur: Check the path state for HP/COMPAQ Smart Array(CCISS) controllers. This is hardware dependent.

none: Does not check the device. Falls back to use values retrieved from sysfs.

The default value is tur.

alias_prefix

This attribute represents the user_friendly_names prefix.

The default value is mpath.

failback

Manages path group failback. Possible values include:

immediate: Specifies immediate failback to the highest priority path group that contains active paths.

manual: Specifies that there is no immediate failback, but that failback can happen only with operator intervention.

followover: Specifies that automatic failback can only be performed when the first path of a path group becomes active. This keeps a node from automatically failing back, when another node requested the failover.

A numeric value greater than zero, specifies deferred failback, and is expressed in seconds.

The default value is manual.

rr_min_io

Specifies the number of I/O requests to route to a path before switching to the next path in the current path group. This setting is only for systems running kernels older than 2.6.31. Newer systems should use rr_min_io_rq. The default value is 1000.

rr_min_io_rq

Specifies the number of I/O requests to route to a path, before switching to the next path in the current path group. Uses a request-based device-mapper-multipath. This setting can be used on systems running current kernels. On systems running kernels older than 2.6.31, use rr_min_io. The default value is 1.

no_path_retry

A numeric value for this attribute specifies the number of times that the path checker must fail for all paths in a multipath device, before disabling queuing.

A value of fail indicates immediate failure, without queuing.

A value of queue indicates that queuing should not stop until the path is fixed.

The default value is fail.

user_friendly_names

Possible values include:

yes: Specifies that the system can use the /etc/multipath/bindings file to assign a persistent and unique alias to the multipath, in the form of mpath<n>.

no: The system uses the WWID as the alias for the multipath. Any device-specific alias you set in the multipaths section of the configuration file, overrides this name.

The default value is no.

queue_without_daemon

If set to no, the multipathd daemon disables queuing for all devices, when it is shut down. The default value is no.

flush_on_last_del

If set to yes, the multipathd daemon disables queuing when the last path to a device is deleted. The default value is no.

max_fds

Sets the maximum number of open file descriptors that can be opened by multipath and the multipathd daemon. This is equivalent to the ulimit -n command. The default value is max, which sets this to the system limit from /proc/sys/fs/nr_open.

checker_timeout

The timeout to use for prioritizers and path checkers that issue SCSI commands with an explicit timeout, in seconds. The sys/block/sd<x>/device/timeout directory contains the default value.

fast_io_fail_tmo

The number of seconds the SCSI layer waits after a problem is detected on an FC remote port, before failing I/O to devices on that remote port. This value must be smaller than the value of dev_loss_tmo. Setting this to off disables the timeout. The default value is 5. The fast_io_fail_tmo option overrides the values of the recovery_tmo and replacement_timeout options of the underlying path devices.

dev_loss_tmo

The number of seconds the SCSI layer waits after a problem is detected on an FC remote port, before removing it from the system. Setting this to infinity will set this to 2147483647 seconds, or 68 years. The operating system determines the default value.

eh_deadline

Specifies the maximum number of seconds the SCSI layer spends performing error handling, when SCSI devices fail. After this timeout, the scsi layer performs a full HBA reset. Setting this is necessary in cases where the rport is never lost, so fast_io_fail_tmo and dev_loss_tmo never trigger, but scsi commands still hang. When the SCSI error handler performs the HBA reset, this affects all target paths on that HBA. The eh_deadline value should only be set in cases where all targets on the affected HBAs are multipathed.

The default value is unset.

detect_prio

If this is set to yes, multipath detects if the device is a SCSI device that supports Asymmetric Logical Unit Access (ALUA), or a NVMe device that supports Asymmetric Namespace Access (ANA). If the device supports ALUA, multipath automatically assigns it the alua prioritizer. If the device supports ANA, multipath automatically assigns it the ana prioritizer.

If detect_prio is set to no, or if the device does not support ALUA or ANA, the prio attribute sets the prioritizer.

The default value is yes.

detect_pgpolicy

If detect_pgpolicy is set to yes and all paths of a multipath device are configured with either the alua or sysfs prioritizer, multipath automatically sets path_grouping_policy to group_by_prio or group_by_tpg.

If detect_pgpolicy is set to no, the path grouping policy is set to failover.

The default value is yes.

detect_pgpolicy_use_tpg

Controls which path grouping policy is set when detect_pgpolicy is set to yes and an ALUA compatible device is detected.

If detect_pgpolicy_use_tpg is set to yes, then detect_pgpolicy sets path_grouping_policy to group_by_tpg.

If detect_pgpolicy_use_tpg is set to no, then detect_pgpolicy sets path_grouping_policy to group_by_prio.

The default value is no.

uid_attribute

Specifies the udev attribute to use for the device WWID.

The default value is device dependent: ID_SERIAL for SCSI devices, ID_UID for DASD devices, and ID_WWN for NVMe devices.

force_sync

If set to yes, this parameter prevents path checkers from running in async mode. This means that only one checker runs at a time. This is useful in cases where many multipathd checkers run in parallel, and can cause significant CPU pressure.

The default value is no.

strict_timing

If set to yes, the multipathd daemon starts a new path checker loop after exactly one second, so that each path check occurs at the exactly set seconds for polling_interval. On busy systems, path checks might take longer than one second. The missing ticks are accounted for in the next round. A warning prints if path checks take longer than the set seconds for polling_interval.

The default value is no.

retrigger_tries, retrigger_delay

Use the retrigger_tries and retrigger_delay parameters in conjunction to make multipathd retrigger uevents. If udev fails to completely process the original uevents, this leaves multipath unable to use the device. The retrigger_tries parameter sets the number of times that multipath tries to retrigger a uevent, in case a device is not completely set up. The retrigger_delay parameter sets the number of seconds between retries. Both of these options accept numbers greater than or equal to 0. Setting the retrigger_tries parameter to 0 disables retries. Setting the retrigger_delay parameter to 0 causes the uevent to be reissued on the next loop of the path checker.

The default value of retrigger_tries is 3. The default value of retrigger_delay is 10.

missing_uev_wait_timeout

This attribute controls the number of seconds the multipathd daemon waits to receive a change event from udev for a newly created multipath device. After that it automatically enables device reloads. In most cases, multipathd delays reloads on a device, until it receives a change uevent from the initial table load.

The default value is 30.

deferred_remove

If set to yes, multipathd performs a deferred remove, instead of a regular remove, when the last path device is deleted. This ensures that if a multipathed device is in use when a regular remove is performed and the remove fails, the device is automatically removed, when the last user closes the device. The default value is no.

san_path_err_threshold, san_path_err_forget_rate, san_path_err_recovery_time

If you set all three of these attributes to integers greater than zero, they enable the multipathd daemon to keep shaky paths from reinstating, by monitoring how frequently the path checker fails. If a path checker fails a path more than the value in the san_path_err_threshold attribute, within san_path_err_forget_rate checks, then the multipathd daemon does not reinstate the path until the value of the san_path_err_recovery_time attribute in seconds passes, without any path checker failures.

See the Shaky paths detection section of the multipath.conf(5) for more information.

The default value is no.

marginal_path_double_failed_time, marginal_path_err_sample_time, marginal_path_err_rate_threshold, marginal_path_err_recheck_gap_time

If marginal_path_double_failed_time, marginal_path_err_rate_threshold, and marginal_path_err_recheck_gap_time are set to integers greater than 0 and marginal_path_err_sample_time is set to an integer greater than 120, they enable the multipathd daemon to keep shaky paths from reinstating, by testing the I/O failure rate of paths that repeatedly fail.

If a path fails twice within the value set in the marginal_path_double_failed_time attribute in seconds, the multipathd daemon does not immediately reinstate it, when the path checker determines that it is back up. Instead, multipathd issues a steady stream of read I/Os to the path for the value set in the marginal_path_err_sample_time attribute in seconds. If there are more than the value set in the marginal_path_err_rate_threshold attribute number of errors per thousand I/Os, multipathd waits for marginal_path_err_recheck_gap_time seconds, and then starts another cycle of testing the path with read I/Os. Otherwise, multipathd reinstates the path.

See the Shaky paths detection section of the multipath.conf(5) for more information.

The default value is no.

marginal_pathgroups

Possible values include:

on: When one of the marginal path detecting methods determines that a path is marginal, the system reinstates the path and places it in a separate pathgroup. This group comes into effect only after all the non-marginal path groups are tried first. This prevents the possibility of IO errors occurring while the system can still use some marginal paths. The path returns to a regular path group as soon as it passes monitoring for a configured time.

off: The delay_*_checks, marginal_path_*, and san_path_err_* attributes keep the system from reinstating any marginal, or shaky paths, until they are monitored for a configured time.

fpin: The multipathd daemon receives fpin notifications, sets path states to marginal, and regroups paths, as described for the on value.

The marginal_path_* and san_path_err_* attributes are implicitly set to no.

See the Shaky paths detection section of the multipath.conf(5) for more information.

The default value is no.

log_checker_err

If set to once, multipathd logs the first path checker error at verbosity level 2. The system logs any further errors at verbosity level 3, until the device is restored. If the log_checker_err parameter is set to always, multipathd always logs the path checker error at verbosity level 2. The default value is always.

skip_kpartx

If set to yes, kpartx does not automatically create partitions on the device. This enables you to create a multipath device, without creating partitions, even if the device has a partition table. The default value of this option is no.

max_sectors_kb

Using this option, you can set the max_sectors_kb device queue parameter to the specified value on all underlying paths of a multipath device, before the first activation of a multipath device. Whenever the system creates a new multipath device, the device inherits the max_sectors_kb value from the path devices. Manually raising this value for the multipath device, or lowering this value for the path devices, can cause multipath to create I/O operations larger than the path devices allow. Using the max_sectors_kb parameter is an easy way to set these values, before the creation of a multipath device on top of the path devices, and prevent passing any invalid-sized I/O operations. If you do not set this parameter, the path devices driver sets it automatically, and the multipath device inherits it from the path devices.

ghost_delay

This attribute sets the number of seconds that multipath waits after creating a device with only ghost paths, before marking it ready for use in systemd. This gives the active paths time to appear before the multipath runs the hardware handler to switch the ghost paths to active ones.

Setting this to 0 or no makes multipath immediately mark a device with only ghost paths as ready.

The default value is no.

enable_foreign

This attribute enables or disables foreign libraries.

The value is a regular expression. Foreign libraries are loaded if their name matches the expression.

By default, no foreign libraries are enabled. Use nvme to enable NVMe native multipath support, or ".*" to enable all foreign libraries.

recheck_wwid

If set to yes, when a failed path is restored, the multipathd daemon rechecks the path WWID. If there is a change in the WWID, the path is removed from the current multipath device, and added again as a new path. The multipathd daemon also checks the path WWID again if it is manually re-added.

This option only works for SCSI devices with configuration to use the default uid_attribute, ID_SERIAL, or sysfs, for getting their WWID.

The default value is no.

remove_retries

This option sets the number of times multipath retries removing a device that is in use. Between each attempt, multipath becomes inactive for 1 second. The default value is 0, which means that multipath does not retry the remove.

detect_checker

If set to yes, multipath checks if the device supports ALUA or Redundant Disk Array Controller (RDAC). If the device supports ALUA, multipath assigns it the tur path_checker. If the device supports RDAC, the multipathd daemon assigns it the rdac path_checker. If the device does not support ALUA or RDAC, or the detect_checker is set to no, the path_checker attribute sets the path checker.

The default value is yes.

reservation_key

The mpathpersist parameter uses this service action reservation key. It must be set for all multipath devices using persistent reservations, and it must be the same as the RESERVATION KEY field of the PERSISTENT RESERVE OUT parameter list, which contains an 8-byte value provided by the application client to the device server to identify the I_T nexus. If you use the --param-aptpl option when registering the key with mpathpersist, you must append :aptpl to the end of the reservation key.

This parameter can also be set to file, which causes mpathpersist to automatically store the RESERVATION KEY used to register the multipath device in the prkeys file. The multipathd daemon then uses this key to register additional paths as they appear. When you remove the registration, this automatically removes the RESERVATION KEY from the prkeys file. It is unset by default. If persistent reservations are necessary, it is recommended to set this attribute to file.

all_tg_pt

If this option is set to yes when mpathpersist registers keys, it treats a registered key from one host to one target port, as going from one host to all target ports. This must be set to yes to successfully use mpathpersist on arrays that automatically set and clear registration keys on all target ports from a host, instead of per target port per host. The default value is no.

auto_resize

Controls when the multipathd command can automatically resize a multipath device. Possible values include:

never: multipathd works without any change. This is the default value.

grow_only: multipathd automatically resizes the multipath device when the device’s paths have grown in size.

grow_shrink: multipathd automatically resizes the multipath device when the device’s paths have either decreased or grown in size.

For more information, see the multipath.conf(5) man page on your system.

4.3. Modifying multipath configuration file defaults
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Customize global DM Multipath behavior by editing the defaults section of the multipath.conf file. Set system-wide values like polling intervals, path selection algorithms, and timeouts to match the needs and performance goals of your storage environment.

Procedure

  1. View the /etc/multipath.conf configuration file, which includes a template of configuration defaults: 

    #defaults {
#       polling_interval        10
#       path_selector           "round-robin 0"
#       path_grouping_policy    multibus
#       uid_attribute           ID_SERIAL
#       prio                    alua
#       path_checker            readsector0
#       rr_min_io               100
#       max_fds                 8192
#       rr_weight               priorities
#       failback                immediate
#       no_path_retry           fail
#       user_friendly_names     yes
#}
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  2. Overwrite the default value for any of the configuration parameters. You can copy the relevant line from this template into the defaults section and uncomment it.

    For example, to overwrite the path_grouping_policy parameter to multibus instead of the default value of failover, copy the appropriate line from the template to the initial defaults section of the configuration file, and uncomment it, as follows: 

    defaults {
        user_friendly_names     yes
        path_grouping_policy    multibus
}
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  3. Validate the /etc/multipath.conf file after modifying the multipath configuration file by running one of the following commands:

    • To display any configuration errors, run: 

      # multipath -t > /dev/null
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    • To display the new configuration with the changes added, run: 

      # multipath -t
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  4. Reload the /etc/multipath.conf file and reconfigure the multipathd daemon for changes to take effect: 

    # service multipathd reload
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4.4. Configuration file multipaths section
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The multipaths section allows customization of specific multipath devices by WWID, overriding global settings with device-specific configurations like aliases and path policies.

Set attributes of individual multipath devices by using the multipaths section of the /etc/multipath.conf configuration file. Device Mapper (DM) Multipath uses these attributes to override all other configuration settings, including those from the overrides section.

The multipaths section recognizes only the multipath subsection as an attribute. The following table shows the attributes that you can set in the multipath subsection, for each specific multipath device. These attributes apply only to one specified multipath. If several multipath subsections match a specific device World Wide Identifier (WWID), the contents of those subsections merge. The settings from latest entries have priority over any previous versions. For more information, see the multipath.conf(5) man page on your system.

Expand
Table 4.2. Multipath subsection attributes
AttributeDescription

wwid

Specifies the WWID of the multipath device, to which the multipath attributes apply. This parameter is mandatory for this section of the multipath.conf file.

alias

Specifies the symbolic name for the multipath device, to which the multipath attributes apply. If you are using user_friendly_names, do not set this value to mpath <n>. This might cause conflicts with an automatically assigned user friendly name, and give you incorrect device node names.

The following example shows multipath attributes specified in the configuration file for two specific multipath devices. The first device has a WWID of 3600508b4000156d70001200000b0000 and a symbolic name of yellow.

The second multipath device in the example has a WWID of 1DEC_321816758474 and a symbolic name of red.

Example 4.1. Multipath attributes specification

multipaths {
       multipath {
              wwid                  3600508b4000156d70001200000b0000
              alias                 yellow
              path_grouping_policy  multibus
              path_selector         "round-robin 0"
              failback              manual
              no_path_retry         5
       }
       multipath {
              wwid                  1DEC_321816758474
              alias                 red
        }
}
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4.5. Configuration file devices section
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The devices section defines configuration settings for specific storage controller types, identified by vendor, product, and revision patterns to optimize multipath behavior per device.

Use the devices section of the multipath.conf configuration file to define settings for individual storage controller types. Values set in this section overwrite specified values in the defaults section.

The system identifies the storage controller types by the vendor, product, and revision keywords. These keywords are regular expressions and must match the sysfs information about the specific device.

The devices section recognizes only the device subsection as an attribute. If there are multiple keyword matches for a device, the attributes of all matching entries apply to it. If an attribute is specified in several matching device subsections, later versions of entries have priority over any previous entries. For more information, see the multipath.conf(5) man page on your system

Important

Configuration attributes in the latest version of the device subsections override attributes in any previous devices subsections and from the defaults section.

The following table shows the attributes that you can set in the device subsection.

Expand
Table 4.3. Devices section attributes
AttributeDescription

vendor

Specifies the regular expression to match the device vendor name. This is a mandatory attribute.

product

Specifies the regular expression to match the device product name. This is a mandatory attribute.

revision

Specifies the regular expression to match the device product revision. If the revision attribute is missing, all device revisions match.

product_blacklist

Multipath uses this attribute to create a device blacklist entry that has a vendor attribute that matches the vendor attribute of this device entry, and a product attribute that matches this product_blacklist attribute.

vpd_vendor

Shows the vendor specific Vital Product Data (VPD) page information, using the VPD page abbreviation.

The multipathd daemon uses this information to gather device specific information. Currently only the hp3par VPD page is supported.

hardware_handler

Specifies the hardware handler to use for a particular device type. All possible values are hardware dependent and include:

emc: Hardware handler for DGC class arrays, as CLARiiON CX/AX and EMC VNX and Unity families.

rdac: Hardware handler for LSI/Engenio/NetApp RDAC class, as NetApp SANtricity E/EF Series, and OEM arrays from IBM DELL SGI STK and SUN.

hp_sw: Hardware handler for HP/COMPAQ/DEC HSG80 and MSA/HSV arrays with Active/Standby mode exclusively.

alua: Hardware handler for SCSI-3 ALUA compatible arrays.

ana: Hardware handler for NVMe ANA compatible arrays.

The default value is unset.

Important

​​Linux kernels, versions 4.3 and newer, automatically attach a device handler to known devices. This includes all devices supporting SCSI-3 ALUA). The kernel does not enable changing the handler later on. Setting the hardware_handler attribute for such devices on these kernels takes no effect.

4.6. Configuration file overrides section
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The overrides section applies configuration changes to all devices, with optional protocol-specific subsections that take precedence over device and default settings.

The overrides section recognizes the optional protocol subsection, and can contain multiple protocol subsections. The system matches path devices against the protocol subsection, using the mandatory type attribute. Attributes in a matching protocol subsection have priority over attributes in the rest of the overrides section. If there are multiple matching protocol subsections, later entries have higher priority. For more information, see the multipath.conf(5) man page on your system.

The protocol subsection recognizes the following mandatory attribute:

Expand
Table 4.4. Protocol subsection attribute
AttributeDescription

type

Specifies the protocol string of the path device. Possible values include:

scsi:fcp, scsi:spi, scsi:ssa, scsi:sbp, scsi:srp, scsi:iscsi, scsi:sas, scsi:adt, scsi:ata, scsi:unspec, ccw, cciss, nvme, undef

This attribute is not a regular expression. The path device protocol string must match exactly.

The attributes in the following list are optional for the protocol subsection. If you do not set them, default values from the overrides, devices or defaults sections apply.

  • fast_io_fail_tmo
  • dev_loss_tmo
  • eh_deadline

4.7. DM Multipath overrides of the device timeout
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The recovery_tmo sysfs option controls the timeout for a particular iSCSI device.

The following options globally override the recovery_tmo values:

  • The replacement_timeout configuration option globally overrides the recovery_tmo value for all iSCSI devices.

  • For all iSCSI devices that are managed by DM Multipath, the fast_io_fail_tmo option in DM Multipath globally overrides the recovery_tmo value.

    The fast_io_fail_tmo option in DM Multipath also overrides the fast_io_fail_tmo option in Fibre Channel devices.

The DM Multipath fast_io_fail_tmo option takes precedence over replacement_timeout. Every time the multipathd service is reloaded, it resets recovery_tmo to the value of the fast_io_fail_tmo configuration option. Use the DM multipath fast_io_fail_tmo configuration option to override recovery_tmo in devices managed by DM Multipath.

4.8. Modifying multipath settings for specific devices
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In the multipaths section of the multipath.conf file, define settings for specific devices using the WWID. These settings override values in overrides, defaults, and devices, letting you fine-tune behavior per device. Multiple entries are allowed.

Procedure

  1. Modify the multipaths section for specific multipath device. The following example shows multipath attributes specified in the configuration file for two specific multipath devices:

    • The first device has a WWID of 3600508b4000156d70001200000b0000 and a symbolic name of yellow.
    • The second multipath device in the example has a WWID of 1DEC_321816758474 and a symbolic name of red.

    In this example, the rr_weight attribute is set to priorities. 

    multipaths {
       multipath {
              wwid                  3600508b4000156d70001200000b0000
              alias                 yellow
              path_grouping_policy  multibus
              path_selector         "round-robin 0"
              failback              manual
              rr_weight             priorities
              no_path_retry         5
       }
       multipath {
              wwid                  1DEC_321816758474
              alias                 red
              rr_weight             priorities
        }
}
    Copy to Clipboard Toggle word wrap

  2. Validate the /etc/multipath.conf file after modifying the multipath configuration file by running one of the following commands:

    • To display any configuration errors, run: 

      # multipath -t > /dev/null
      Copy to Clipboard Toggle word wrap

    • To display the new configuration with the changes added, run: 

      # multipath -t
      Copy to Clipboard Toggle word wrap

  3. Reload the /etc/multipath.conf file and reconfigure the multipathd daemon for changes to take effect: 

    # service multipathd reload
    Copy to Clipboard Toggle word wrap

4.9. Modifying the multipath configuration for specific devices with protocol
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You can Use the protocol subsection in the overrides section of /etc/multipath.conf to set path-specific options by transport type. These settings override values in overrides, devices, and defaults and apply only to matching type values.

Prerequisites

  • You have configured Device Mapper (DM) multipath in your system.
  • You have multipath devices where not all paths use the same transport protocol.

Procedure

  1. View the specific path protocol by running the following: 

    # multipathd show paths format "%d %P"
dev protocol
sda scsi:ata
sdb scsi:fcp
sdc scsi:fcp
    Copy to Clipboard Toggle word wrap

  2. Edit the overrides section of the /etc/multipath.conf file, by adding protocol subsections for each multipath type.

    The overrides section can include multiple protocol subsections.

    Important

    The protocol subsection must include a type parameter. The configuration of all paths with a matching type parameter is then updated with the rest of the parameters listed in the protocol subsection.

    • Settings for path devices, which use the scsi:fcp protocol: 

      overrides {
        dev_loss_tmo 60
        fast_io_fail_tmo 8
        protocol {
                type "scsi:fcp"
                dev_loss_tmo 70
                fast_io_fail_tmo 10
                eh_deadline 360
        }
}
      Copy to Clipboard Toggle word wrap

    • Settings for path devices, which use the scsi:iscsi protocol: 

      overrides {
        dev_loss_tmo 60
        fast_io_fail_tmo 8
        protocol {
                type "scsi:iscsi"
                dev_loss_tmo 60
                fast_io_fail_tmo 120
        }
}
      Copy to Clipboard Toggle word wrap

    • Settings for path devices, which use all other protocols: 

      overrides {
        dev_loss_tmo 60
        fast_io_fail_tmo 8
        protocol {
                type "<type of protocol>"
                dev_loss_tmo 60
                fast_io_fail_tmo 8
        }
}
      Copy to Clipboard Toggle word wrap

4.10. Modifying multipath settings for storage controllers
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Customize DM Multipath settings for specific storage vendors and models in the devices section of multipath.conf. These attributes optimize performance and override defaults, unless replaced by values in multipaths or overrides for matching paths.

Procedure

  1. View the information about the default configuration value, including supported devices: 

    # multipathd show config
# multipath -t
    Copy to Clipboard Toggle word wrap

    Many devices that support multipathing are included by default in a multipath configuration.

  2. Optional: If you need to modify the default configuration values, you can overwrite the default values by including an entry in the configuration file for the device that overwrites those values. You can copy the device configuration defaults for the device that the multipathd show config command displays and override the values that you want to change.

  3. Add a device that is not configured automatically by default to the devices section of the configuration file by setting the vendor and product parameters. Find these values by opening the /sys/block/device_name/device/vendor and /sys/block/device_name/device/model files where device_name is the device to be multipathed, as mentioned in the following example: 

    # cat /sys/block/sda/device/vendor
WINSYS
# cat /sys/block/sda/device/model
SF2372
    Copy to Clipboard Toggle word wrap

  4. Optional: Specify the additional parameters depending on your specific device:

    active/active device
    Usually there is no need to set additional parameters in this case. If required, you might set path_grouping_policy to multibus. Other parameters you may need to set are no_path_retry and rr_min_io.
    active/passive device
    If it automatically switches paths with I/O to the passive path, you need to change the checker function to one that does not send I/O to the path to test if it is working, otherwise, your device will keep failing over. This means that you have set the path_checker to tur, which works for all SCSI devices that support the Test Unit Ready command, which most do.

    If the device needs a special command to switch paths, then configuring this device for multipath requires a hardware handler kernel module. The current available hardware handler is emc. If this is not sufficient for your device, you might not be able to configure the device for multipath.

    The following example shows a device entry in the multipath configuration file: 

    #	}
#	device {
#		vendor			"COMPAQ  "
#		product			"MSA1000         "
#		path_grouping_policy	multibus
#		path_checker		tur
#		rr_weight		priorities
#	}
#}
    Copy to Clipboard Toggle word wrap

  5. Validate the /etc/multipath.conf file after modifying the multipath configuration file by running one of the following commands:

    • To display any configuration errors, run: 

      # multipath -t > /dev/null
      Copy to Clipboard Toggle word wrap

    • To display the new configuration with the changes added, run: 

      # multipath -t
      Copy to Clipboard Toggle word wrap

  6. Reload the /etc/multipath.conf file and reconfigure the multipathd daemon for changes to take effect: 

    # service multipathd reload
    Copy to Clipboard Toggle word wrap

4.11. Setting multipath values for all devices
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Use the overrides section in multipath.conf to apply global settings to all devices, ensuring consistent path management, timeouts, and other parameters. These values override defaults and devices, unless replaced in the multipaths section.

Procedure

  1. Override device specific settings. For example, you might want all devices to set no_path_retry to fail. Use the following command to turn off queueing, when all paths have failed. This overrides any device specific settings. 

    overrides {
        no_path_retry fail
}
    Copy to Clipboard Toggle word wrap

  2. Validate the /etc/multipath.conf file after modifying the multipath configuration file by running one of the following commands:

    • To display any configuration errors, run: 

      # multipath -t > /dev/null
      Copy to Clipboard Toggle word wrap

    • To display the new configuration with the changes added, run: 

      # multipath -t
      Copy to Clipboard Toggle word wrap

  3. Reload the /etc/multipath.conf file and reconfigure the multipathd daemon for changes to take effect: 

    # service multipathd reload
    Copy to Clipboard Toggle word wrap

Chapter 5. Preventing devices from multipathing
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You can configure DM Multipath to ignore selected devices when it configures multipath devices. DM Multipath does not group these ignored devices into a multipath device.

5.1. Conditions when DM Multipath creates a multipath device for a path
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DM Multipath uses the find_multipaths parameter and device discovery rules to automatically determine when to create multipath devices for detected storage paths.

DM Multipath has a set of default rules to determine whether to create a multipath device for a path or whether to ignore the path. You can configure the behavior.

If the find_multipaths configuration parameter is set to off, multipath always tries to create a multipath device for every path that is not explicitly disabled. If the find_multipaths configuration parameter is set to on, then multipath creates a device, only if one of following conditions is met:

  • There are at least two paths with the same World-Wide Identification (WWID) that are not disabled.
  • You manually force the creation of the device by specifying a device with the multipath command.
  • A path has the same WWID as a multipath device that was previously created even if that multipath device does not currently exist. Whenever a multipath device is created, multipath remembers the WWID of the device so that it automatically creates the device again as soon as it sees a path with that WWID. This allows you to have multipath automatically choose the correct paths to make into multipath devices, without having to disable multipathing on other devices.

If you have previously created a multipath device without using the find_multipaths parameter and then you later set the parameter to on, you might need to remove the WWIDs of any device you do not want created as a multipath device from the /etc/multipath/wwids file. The following example shows a sample /etc/multipath/wwids file. The WWIDs are enclosed by slashes (/): 

# Multipath wwids, Version : 1.0
# NOTE: This file is automatically maintained by multipath and multipathd.
# You should not need to edit this file in normal circumstances.
#
# Valid WWIDs:
/3600d0230000000000e13955cc3757802/
/3600d0230000000000e13955cc3757801/
/3600d0230000000000e13955cc3757800/
/3600d02300069c9ce09d41c31f29d4c00/
/SWINSYS  SF2372         0E13955CC3757802/
/3600d0230000000000e13955cc3757803/
Copy to Clipboard Toggle word wrap

In addition to on and off, you can also set find_multipaths to the following values:

strict
Multipath never accepts paths that have not previously been multipathed and are therefore not in the /etc/multipath/wwids file.
smart
Multipath always accepts non-disabled devices in udev as soon as they appear. If multipathd does not create the device within a timeout set with the find_multipaths_timeout parameter, it will release its claim on the device.

The built-in default value of find_multipaths is off. The default multipath.conf file created by mpathconf, however, will set the value of find_multipaths to on.

When the find_multipaths parameter is set to on, disable multipathing only on the devices with multiple paths that you do not want to be multipathed. Because of this, it will generally not be necessary to disable multipathing on devices.

If you add a previously created multipath device to blacklist, removing the WWID of that device from the /etc/multipath/wwids file by using the -w option can help avoid issues with other programs. For example, to remove the device /dev/sdb with WWID 3600d0230000000000e13954ed5f89300 from the /etc/multipath/wwids file, you can use either of the following methods.

  • Removing a multipath device by using the device name. 

    # multipath -w /dev/sdb
wwid '3600d0230000000000e13954ed5f89300' removed
    Copy to Clipboard Toggle word wrap

  • Removing a multipath device by using the WWID of the device. 

    # multipath -w 3600d0230000000000e13954ed5f89300
wwid '3600d0230000000000e13954ed5f89300' removed
    Copy to Clipboard Toggle word wrap

You can also use the -W option to update the /etc/multipath/wwids file. This would reset the /etc/multipath/wwids file to only include the WWIDs of the current multipath devices. To reset the file, run the following: 

# multipath -W
successfully reset wwids
Copy to Clipboard Toggle word wrap

5.2. Criteria for disabling multipathing on certain devices
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Device exclusion from multipathing uses criteria such as, WWID, device name, type, property, or protocol, evaluated in priority order with exception lists taking precedence.

You can disable multipathing on devices by any of the following criteria:

  • WWID
  • device name
  • device type
  • property
  • protocol
Note

By default, a variety of device types are disabled, even after you comment out the initial blacklist section of the configuration file.

For every device, DM Multipath evaluates these criteria in the following order:

  1. property
  2. devnode
  3. device
  4. protocol
  5. wwid

If a device turns out to be disabled by any of the mentioned criteria, DM Multipath excludes it from handling by multipathd, and does not evaluate the later criteria. For each criteria, the exception list takes precedence over the list of disabled devices, if a device matches both.

5.3. Disabling multipathing by WWID
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Exclude specific devices from multipath by disabling them by using their WWID in the multipath.conf file. This is useful for local disks, single-path devices, or storage needing special handling outside the multipath framework.

Procedure

  1. Find WWID of a device: 

    # multipathd show paths raw format "%d %w" | grep sdb
sdb 3600508b4001080520001e00011700000
    Copy to Clipboard Toggle word wrap

  2. Disable devices in the /etc/multipath.conf configuration file by using the wwid entry.

    The following example shows the lines in the DM Multipath configuration file that disable a device with a WWID of 3600508b4001080520001e00011700000: 

    blacklist {
       wwid 3600508b4001080520001e00011700000
}
    Copy to Clipboard Toggle word wrap

  3. Validate the /etc/multipath.conf file after modifying the multipath configuration file by running one of the following commands:

    • To display any configuration errors, run: 

      # multipath -t > /dev/null
      Copy to Clipboard Toggle word wrap

    • To display the new configuration with the changes added, run: 

      # multipath -t
      Copy to Clipboard Toggle word wrap

  4. Reload the /etc/multipath.conf file and reconfigure the multipathd daemon for changes to take effect: 

    # service multipathd reload
    Copy to Clipboard Toggle word wrap

5.4. Disabling multipathing by device name
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Disable multipathing for specific devices by using their device names, such as /dev/sda in the multipath.conf file. This prevents DM Multipath from grouping local disks, USB devices, or other storage into multipath devices, keeping them as individual block devices.

Procedure

  1. Display device information: 

    # udevadm info --query=all -n /dev/mapper/sd*
    Copy to Clipboard Toggle word wrap

  2. Disable devices in the /etc/multipath.conf configuration file by using the devnode entry.

    The following example shows the lines in the DM Multipath configuration file that disable all SCSI devices, because it disables all sd* devices as well: 

    blacklist {
       devnode "^sd[a-z]"
}
    Copy to Clipboard Toggle word wrap

    You can use a devnode entry to disable individual devices rather than all devices of a specific type. However, this is not recommended because unless it is statically mapped by udev rules, there is no guarantee that a specific device will have the same name on reboot. For example, a device name could change from /dev/sda to /dev/sdb on reboot.

    By default, DM Multipath disables all devices that are not SCSI, NVMe, or DASD, by using the following devnode entry: 

    blacklist {
       devnode "!^(sd[a-z]|dasd[a-z]|nvme[0-9])"
}
    Copy to Clipboard Toggle word wrap

    The devices that this entry disables do not generally support DM Multipath.

  3. Validate the /etc/multipath.conf file after modifying the multipath configuration file by running one of the following commands:

    • To display any configuration errors, run: 

      # multipath -t > /dev/null
      Copy to Clipboard Toggle word wrap

    • To display the new configuration with the changes added, run: 

      # multipath -t
      Copy to Clipboard Toggle word wrap

  4. Reload the /etc/multipath.conf file and reconfigure the multipathd daemon for changes to take effect: 

    # service multipathd reload
    Copy to Clipboard Toggle word wrap

5.5. Disabling multipathing by device type
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Exclude entire categories of devices from multipath by specifying vendor and product info in the device section of multipath.conf. This prevents DM Multipath from grouping devices of certain models or vendors, keeping them as individual block devices.

Procedure

  1. Display device type: 

    # multipathd show paths raw format "%d %s" | grep sdb
sdb HP,HSV210
    Copy to Clipboard Toggle word wrap

  2. Disable devices in the /etc/multipath.conf configuration file by using the device section.

    The following example disables multipathing on all IBM DS4200 and HP devices: 

    blacklist {
       device {
               vendor  "IBM"
               product "3S42"       #DS4200 Product 10
       }
       device {
               vendor  "HP"
               product ".*"
       }
}
    Copy to Clipboard Toggle word wrap

  3. Validate the /etc/multipath.conf file after modifying the multipath configuration file by running one of the following commands:

    • To display any configuration errors, run: 

      # multipath -t > /dev/null
      Copy to Clipboard Toggle word wrap

    • To display the new configuration with the changes added, run: 

      # multipath -t
      Copy to Clipboard Toggle word wrap

  4. Reload the /etc/multipath.conf file and reconfigure the multipathd daemon for changes to take effect: 

    # service multipathd reload
    Copy to Clipboard Toggle word wrap

5.6. Disabling multipathing by udev property
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Exclude devices from multipath using their udev properties in the multipath.conf file. This method allows flexible filtering based on system-detected attributes like hardware type or connection, giving precise control over which devices are excluded from multipathing.

Procedure

  1. Display the udev variables for a device: 

    # udevadm info --query=all -n /dev/sdb
    Copy to Clipboard Toggle word wrap

  2. Disable devices in the /etc/multipath.conf configuration file by using the property parameter. This parameter is a regular expression string that matches against the udev environment variable name for the devices.

    The following example disables multipathing on all devices with the udev property ID_ATA: 

    blacklist {
        property "ID_ATA"
}
    Copy to Clipboard Toggle word wrap

  3. Validate the /etc/multipath.conf file after modifying the multipath configuration file by running one of the following commands:

    • To display any configuration errors, run: 

      # multipath -t > /dev/null
      Copy to Clipboard Toggle word wrap

    • To display the new configuration with the changes added, run: 

      # multipath -t
      Copy to Clipboard Toggle word wrap

  4. Reload the /etc/multipath.conf file and reconfigure the multipathd daemon for changes to take effect: 

    # service multipathd reload
    Copy to Clipboard Toggle word wrap

5.7. Disabling multipathing by device protocol
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Exclude devices from multipath based on their transport protocol by using the device protocol setting in multipath.conf. This is useful for preventing multipathing on local or specific protocols better managed outside the multipath framework. sa .Procedure

  1. Optional: View the protocol that a path is using: 

    # multipathd show paths raw format "%d %P" | grep sdb
sdb scsi:fcp
    Copy to Clipboard Toggle word wrap

  2. Disable devices in the /etc/multipath.conf configuration file by using the protocol parameter.

    The protocol parameter takes a regular expression and blacklists all devices with matching protocol strings. For example, to disable multipathing on all nvme devices, use the following: 

    blacklist {
        protocol "nvme"
}
    Copy to Clipboard Toggle word wrap

    DM Multipath recognizes the protocol strings such as scsi:fcp, scsi:spi, scsi:ssa, scsi:sbp, scsi:srp, scsi:iscsi, scsi:sas, scsi:adt, scsi:ata, scsi:unspec, ccw, cciss, nvme:pcie, nvme:rdma, nvme:fc, nvme:tcp, nvme:loop, nvme:apple-nvme, nvme:unspec, and undef.

  3. Validate the /etc/multipath.conf file after modifying the multipath configuration file by running one of the following commands:

    • To display any configuration errors, run: 

      # multipath -t > /dev/null
      Copy to Clipboard Toggle word wrap

    • To display the new configuration with the changes added, run: 

      # multipath -t
      Copy to Clipboard Toggle word wrap

  4. Reload the /etc/multipath.conf file and reconfigure the multipathd daemon for changes to take effect: 

    # service multipathd reload
    Copy to Clipboard Toggle word wrap

5.8. Adding exceptions for devices with disabled multipathing
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Re-enable multipathing for specific devices by adding exceptions in multipath.conf. This is useful when broad exclusion rules are in place but certain devices still require multipathing, allowing precise control over which devices are managed by DM Multipath.

Prerequisites

  • Multipathing is disabled on certain devices.

Procedure

  1. Enable multipathing on the devices by using the blacklist_exceptions section of the /etc/multipath.conf configuration file.

    When specifying devices in the blacklist_exceptions section of the configuration file, you must specify the exceptions by using the same criteria as they were specified in the blacklist section. For example, a WWID exception does not apply to devices disabled by a devnode entry, even if the disabled device is associated with that WWID. Similarly, devnode exceptions apply only to devnode entries, and device exceptions apply only to device entries.

    Following is an example for adding exceptions for devices with disabled multipathing

    • An exception by WWID

      If you have a large number of devices and want to multipath only one of them with the WWID of 3600d0230000000000e13955cc3757803, instead of individually disabling each of the devices except the one you want, you could disable all of them, and then enable only the one you want by adding the following lines to the /etc/multipath.conf file: 

      blacklist {
        wwid ".*"
}

blacklist_exceptions {
        wwid "3600d0230000000000e13955cc3757803"
}
      Copy to Clipboard Toggle word wrap

      Alternatively, you could use an exclamation mark (!) to invert the blacklist entry, which disables all devices except the specified WWID: 

      blacklist {
        wwid "!3600d0230000000000e13955cc3757803"
}
      Copy to Clipboard Toggle word wrap

    • An exception by udev property

      The property parameter works differently than the other blacklist_exception parameters. The value of the property parameter must match the name of a variable in the udev database. Otherwise, the device is disabled. Using this parameter, you can disable multipathing on certain SCSI devices, such as USB sticks and local hard drives.

      To enable multipathing only on SCSI devices that could reasonably be multipathed, set this parameter to (SCSI_IDENT_|ID_WWN) as in the following example: 

      blacklist_exceptions {
        property "(SCSI_IDENT_|ID_WWN)"
}
      Copy to Clipboard Toggle word wrap

  2. Validate the /etc/multipath.conf file after modifying the multipath configuration file by running one of the following commands:

    • To display any configuration errors, run: 

      # multipath -t > /dev/null
      Copy to Clipboard Toggle word wrap

    • To display the new configuration with the changes added, run: 

      # multipath -t
      Copy to Clipboard Toggle word wrap

  3. Reload the /etc/multipath.conf file and reconfigure the multipathd daemon for changes to take effect: 

    # service multipathd reload
    Copy to Clipboard Toggle word wrap

Chapter 6. Managing multipathed volumes
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You can manage multipath volumes by using the multipath, dmsetup, and multipathd commands, which are provided by DM Multipath to resize devices, move file systems, and administer the multipathd daemon.

6.1. Resizing an online multipath device
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Resize an online multipath device and its filesystem using the multipathd and resize2fs commands. This allows you to expand storage capacity without downtime, ensuring applications remain available while scaling to meet growing data needs.

Procedure

  1. Resize your physical device.

  2. Find the paths to the logical unit number (LUN): 

    # multipath -l
    Copy to Clipboard Toggle word wrap

  3. Resize your paths. For SCSI devices, writing a 1 to the rescan file for the device causes the SCSI driver to rescan, as in the following command: 

    # echo 1 > /sys/block/path_device/device/rescan
    Copy to Clipboard Toggle word wrap

    Ensure that you run this command for each of the path devices. For example, if your path devices are sda, sdb, sde, and sdf, run the following commands: 

    # echo 1 > /sys/block/sda/device/rescan
# echo 1 > /sys/block/sdb/device/rescan
# echo 1 > /sys/block/sde/device/rescan
# echo 1 > /sys/block/sdf/device/rescan
    Copy to Clipboard Toggle word wrap

  4. Resize your multipath device: 

    # multipathd resize map multipath_device
    Copy to Clipboard Toggle word wrap

  5. Resize the file system, assuming no LVM or DOS partitions are used: 

    # resize2fs /dev/mapper/mpatha
    Copy to Clipboard Toggle word wrap

6.2. Moving a root file system from a single path device to a multipath device
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Move the root filesystem from a single-path device to a multipath setup to ensure path redundancy for critical system data. This enhances reliability by allowing the system to boot and operate even if one storage path fails, improving overall availability.

Prerequisites

  • You have installed the device-mapper-multipath package.

Procedure

  1. Create the /etc/multipath.conf configuration file: 

    # mpathconf --enable
    Copy to Clipboard Toggle word wrap

  2. Enable the multipathd service: 

    # systemctl enable multipathd.service
    Copy to Clipboard Toggle word wrap
  3. If the find_multipaths configuration parameter is not set to on, edit the blacklist and blacklist_exceptions sections of the /etc/multipath.conf file, as described in Preventing devices from multipathing.

  4. Add the WWID of the device to the /etc/multipath/wwids file: 

    # multipath -a /dev/sdb
wwid '3600d02300069c9ce09d41c4ac9c53200' added
    Copy to Clipboard Toggle word wrap

    Replace /dev/sdb with the root device name.

  5. Confirm that your configuration file is set up correctly: 

    # multipath -d 3600d02300069c9ce09d41c4ac9c53200
: mpatha (3600d02300069c9ce09d41c4ac9c53200) undef 3PARdata,VV
size=446M features='1 queue_if_no_path' hwhandler='1 alua' wp=undef
`-+- policy='service-time 0' prio=50 status=undef
  `- 5:0:0:0 sdb 8:16 undef ready running
    Copy to Clipboard Toggle word wrap

    Replace 3600d02300069c9ce09d41c4ac9c53200 with the WWID of your swap device.

  6. Rebuild the initramfs file system with multipath: 

    # dracut --force --add multipath
    Copy to Clipboard Toggle word wrap
  7. Shut the machine down.
  8. Boot the machine.
  9. Make the other paths visible to the machine.

Verification

  • Check if the multipath device is created by running the following command: 

    # multipath -l | grep 3600d02300069c9ce09d41c4ac9c53200
mpatha (3600d02300069c9ce09d41c4ac9c53200) dm-0 3PARdata,VV
    Copy to Clipboard Toggle word wrap

6.3. Moving a swap file system from a single path device to a multipath device
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Move swap file system from single-path to multipath storage to ensure redundancy and prevent performance issues. If swap uses LVM, no special steps are needed, but non-LVM swap devices may require editing /etc/fstab to use the correct multipath device name.

Procedure

  1. Create the /etc/multipath.conf configuration file: 

    # mpathconf --enable
    Copy to Clipboard Toggle word wrap

  2. Enable the multipathd service: 

    # systemctl enable multipathd.service
    Copy to Clipboard Toggle word wrap
  3. If the find_multipaths configuration parameter is not set to on, edit the blacklist and blacklist_exceptions sections of the /etc/multipath.conf file, as described in Preventing devices from multipathing.

  4. Add the WWID of the device to the /etc/multipath/wwids file: 

    # multipath -a /dev/sdb
wwid '3600d02300069c9ce09d41c4ac9c53200' added
    Copy to Clipboard Toggle word wrap

    Replace /dev/sdb with the swap device name.

  5. Confirm that your configuration file is set up correctly: 

    # multipath -d 3600d02300069c9ce09d41c4ac9c53200
: mpatha (3600d02300069c9ce09d41c4ac9c53200) undef 3PARdata,VV
size=446M features='1 queue_if_no_path' hwhandler='1 alua' wp=undef
`-+- policy='service-time 0' prio=50 status=undef
  `- 5:0:0:0 sdb 8:16 undef ready running
    Copy to Clipboard Toggle word wrap

    Replace 3600d02300069c9ce09d41c4ac9c53200 with the WWID of your swap device.

  6. Set up an alias for the swap device in the /etc/multipath.conf file: 

    multipaths {
    multipath {
        wwid WWID_of_swap_device
        alias swapdev
    }
}
    Copy to Clipboard Toggle word wrap

  7. Edit the /etc/fstab file and replace the old device path to the root device with the multipath device.

    For example, if you had the following entry in the /etc/fstab file: 

    /dev/sdb2 swap                    swap    defaults        0 0
    Copy to Clipboard Toggle word wrap

    Change the entry to the following: 

    /dev/mapper/swapdev swap          swap    defaults        0 0
    Copy to Clipboard Toggle word wrap

  8. Rebuild the initramfs file system with multipath: 

    # dracut --force --add multipath
    Copy to Clipboard Toggle word wrap
  9. Shut the machine down.
  10. Boot the machine.
  11. Make the other paths visible to the machine.

Verification

  • Verify if the swap device is on the multipath device: 

    # swapon -s

Filename                Type          Size Used    Priority
/dev/dm-3               partition     4169724 0    -2
    Copy to Clipboard Toggle word wrap

    The file name should match the multipath swap device. 

    # readlink -f /dev/mapper/swapdev
/dev/dm-3
    Copy to Clipboard Toggle word wrap

6.4. Determining device mapper entries for multipath devices
Copia collegamento

Identify device mapper entries for configured multipath devices by using the multipathd command. This helps link multipath device names to their underlying device mapper entries, aiding in monitoring, troubleshooting, and system administration tasks for accurate device identification.

Procedure

  • Display all device mapper devices: 

    # multipathd show maps format "%n %d"

name   sysfs
mpathd dm-4
mpathb dm-3
mpatha dm-2
mpathh dm-9
    Copy to Clipboard Toggle word wrap

6.5. Administering the multipathd daemon
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Manage and interact with the multipathd daemon using its commands. Administering multipathd is essential for monitoring path status, viewing device info, and controlling multipath behavior in real-time without needing service restarts or system reboots.

Procedure

  • View the default format for the output of the multipathd show maps command: 

    # multipathd show maps
name sysfs uuid
mpathc dm-0 360a98000324669436c2b45666c567942
    Copy to Clipboard Toggle word wrap

  • Some multipathd commands include a format option followed by a wildcard. Display a list of available wildcards with the following command: 

    # multipathd show wildcards
multipath format wildcards:
%n  name
%w  uuid
%d  sysfs
...
    Copy to Clipboard Toggle word wrap

  • Display the multipath devices that multipathd is monitoring. Use wildcards to specify the shown fields: 

    # multipathd show maps format "%n %w %d %s"
name   uuid                              sysfs vend/prod/rev
mpathc 360a98000324669436c2b45666c567942 dm-0  NETAPP,LUN
    Copy to Clipboard Toggle word wrap

  • Display the paths that multipathd is monitoring. Use wildcards to specify the shown fields: 

    # multipathd show paths format "%n %w %d %s"
target WWNN        uuid                              dev vend/prod/rev
0x50001fe1500d2250 3600508b4001080520001e00011700000 sdb HP,HSV210
    Copy to Clipboard Toggle word wrap

  • Display data in a raw format: 

    # multipathd show maps raw format "%n %w %d %s"
mpathc 360a98000324669436c2b45666c567942 dm-0 NETAPP,LUN
    Copy to Clipboard Toggle word wrap

    In raw format, no headers are printed and the fields are not padded to align the columns with the headers. This output can be more easily used for scripting.

Chapter 7. Removing storage devices
Copia collegamento

You can safely remove a storage device from a running system, which helps prevent system memory overload and data loss.

Do not remove a storage device on a system where:

  • Free memory is less than 5% of the total memory in more than 10 samples per 100.
  • Swapping is active (non-zero si and so columns in the vmstat command output).

7.1. Prerequisites
Copia collegamento

  • Before you remove a storage device, ensure that you have enough free system memory due to the increased system memory load during an I/O flush. Use the following commands to view the current memory load and free memory of the system: 

    # vmstat 1 100
# free
    Copy to Clipboard Toggle word wrap

7.2. Safe removal of storage devices
Copia collegamento

Safely removing a storage device from a running system requires a top-to-bottom approach. Start from the top layer, which typically is an application or a file system, and work towards the bottom layer, which is the physical device.

You can use storage devices in multiple ways, and they can have different virtual configurations on top of physical devices. For example, you can group multiple instances of a device into a multipath device, make it part of a RAID, or you can make it part of an LVM group. Additionally, devices can be accessed via a file system, or they can be accessed directly such as a "raw" device.

While using the top-to-bottom approach, you must ensure that:

  • the device that you want to remove is not in use
  • all pending I/O to the device is flushed
  • the operating system is not referencing the storage device

7.3. Removing block devices and associated metadata
Copia collegamento

To safely remove a block device from a running system and avoid memory overload or data loss, remove its metadata first. Address each layer, starting with the filesystem down to the disk—to ensure the system remains stable and in a consistent state.

Prerequisites

  • You have an existing block device stack containing the file system, the logical volume, and the volume group.
  • You ensured that no other applications or services are using the device that you want to remove.
  • You backed up the data from the device that you want to remove.

  • Optional: If you want to remove a multipath device, and you are unable to access its path devices, disable queueing of the multipath device by running the following command: 

    # multipathd disablequeueing map multipath-device
    Copy to Clipboard Toggle word wrap

    This enables the I/O of the device to fail, allowing the applications that are using the device to shut down.

Note

Removing devices with their metadata one layer at a time ensures no stale signatures remain on the disk.

Use specific commands depending on what type of devices you are removing:

  • For LVM, run lvremove, vgremove, and pvremove.
  • For software RAID, run mdadm to remove the array. For more information, see Managing RAID.
  • For block devices encrypted by using LUKS, there are specific additional steps. The following procedure will not work for the block devices encrypted by using LUKS. For more information, see Encrypting block devices by using LUKS.
Warning

Rescanning the SCSI bus or performing any other action that changes the state of the operating system, without following the procedure documented here can cause delays due to I/O timeouts, devices to be removed unexpectedly, or data loss.

Procedure

  1. Unmount the file system: 

    # umount /mnt/mount-point
    Copy to Clipboard Toggle word wrap

  2. Remove the file system: 

    # wipefs -a /dev/vg0/myvol
    Copy to Clipboard Toggle word wrap

    If you have added an entry into the /etc/fstab file to make a persistent association between the file system and a mount point, edit /etc/fstab at this point to remove that entry.

    Continue with the following steps, depending on the type of the device you want to remove:

  3. Remove the logical volume (LV) that contained the file system: 

    # lvremove vg0/myvol
    Copy to Clipboard Toggle word wrap

  4. If there are no other logical volumes remaining in the volume group (VG), you can safely remove the VG that contained the device: 

    # vgremove vg0
    Copy to Clipboard Toggle word wrap

  5. Remove the physical volume (PV) metadata from the PV device(s): 

    # pvremove /dev/sdc1
    Copy to Clipboard Toggle word wrap 
    # wipefs -a /dev/sdc1
    Copy to Clipboard Toggle word wrap

  6. Remove the partitions that contained the PVs: 

    # parted /dev/sdc rm 1
    Copy to Clipboard Toggle word wrap

  7. Remove the partition table if you want to fully wipe the device: 

    # wipefs -a /dev/sdc
    Copy to Clipboard Toggle word wrap

  8. Execute the following steps only if you want to physically remove the device:

    • If you are removing a multipath device, execute the following commands:

      1. View all the paths to the device: 

        # multipath -l
        Copy to Clipboard Toggle word wrap

        The output of this command is required in a later step.

      2. Flush the I/O and remove the multipath device: 

        # multipath -f multipath-device
        Copy to Clipboard Toggle word wrap

    • If the device is not configured as a multipath device, or if the device is configured as a multipath device and you have previously passed I/O to the individual paths, flush any outstanding I/O to all device paths that are used: 

      # blockdev --flushbufs device
      Copy to Clipboard Toggle word wrap

      This is important for devices accessed directly where the umount or vgreduce commands do not flush the I/O.

    • If you are removing a SCSI device, execute the following commands:

      1. Remove any reference to the path-based name of the device, such as /dev/sd, /dev/disk/by-path, or the major:minor number, in applications, scripts, or utilities on the system. This ensures that different devices added in the future are not mistaken for the current device.

      2. Remove each path to the device from the SCSI subsystem: 

        # echo 1 > /sys/block/device-name/device/delete
        Copy to Clipboard Toggle word wrap

        Here the device-name is retrieved from the output of the multipath -l command, if the device was previously used as a multipath device.

  9. Remove the physical device from a running system. Note that the I/O to other devices does not stop when you remove this device.

Verification

  • Verify that the devices you intended to remove are not displaying on the output of lsblk command. The following is an example output: 

    # lsblk

NAME   MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sda      8:0    0    5G  0 disk
sr0     11:0    1 1024M  0 rom
vda    252:0    0   10G  0 disk
|-vda1 252:1    0    1M  0 part
|-vda2 252:2    0  100M  0 part /boot/efi
`-vda3 252:3    0  9.9G  0 part /
    Copy to Clipboard Toggle word wrap

Chapter 8. Troubleshooting DM Multipath
Copia collegamento

Troubleshoot multipath configuration issues by checking daemon status, queue_if_no_path feature problems, and using the multipathd interactive console for diagnostics.

The following issues may result in a slow or non-functioning multipath configuration:

The multipath daemon is not running
If you find you have trouble implementing a multipath configuration, ensure that the multipathd daemon is running, as described in Configuring DM Multipath. The multipathd daemon must be running to use multipathed devices.
Issues with queue_if_no_path feature
If a multipath device is configured with the features "1 queue_if_no_path" option, then any process that issues I/O hangs until one or more paths are restored.

8.1. Troubleshooting issues with queue_if_no_path feature
Copia collegamento

Resolve I/O hangs from queue_if_no_path by setting no_path_retry N in /etc/multipath.conf, limiting retries when all paths fail. You can also disable queueing at runtime for specific LUNs to prevent applications from hanging during path outages.

Procedure

  1. Disable queueing:

    • For a specific device: 

      # multipathd disablequeueing map device
      Copy to Clipboard Toggle word wrap

    • For all devices: 

      # multipathd disablequeueing maps
      Copy to Clipboard Toggle word wrap

      After you disable queueing, it will remain disabled until you restart or reload multipathd.

  2. Reset queueing to a previous value:

    • For a specific device: 

      # multipathd restorequeueing map device
      Copy to Clipboard Toggle word wrap

    • For all devices: 

      # multipathd restorequeueing maps
      Copy to Clipboard Toggle word wrap

8.2. Troubleshooting with the multipathd interactive console
Copia collegamento

Use the multipathd -k interactive console to troubleshoot multipath issues in real time. This console provides access to status info, config details, and control commands. Type help for commands and press Ctrl+D to exit without disrupting services.

Procedure

  1. Display the multipath configuration, including the default values, before exiting the console: 

    # multipathd -k
multipathd> show config
multipathd> Ctrl+D
    Copy to Clipboard Toggle word wrap

  2. Ensure that multipath picked up all changes to the multipath.conf file: 

    # multipathd -k
multipathd> reconfigure
multipathd> Ctrl+D
    Copy to Clipboard Toggle word wrap

  3. Ensure that the path checker is working properly: 

    # multipathd -k
multipathd> show paths
multipathd> Ctrl+D
    Copy to Clipboard Toggle word wrap

  4. You can also run a single multipathd interactive command directly from the command line, without starting the interactive console. For example, to check that multipath picks up all changes to the multipath.conf file, run the following command: 

    # multipathd reconfigure
    Copy to Clipboard Toggle word wrap

You can configure the maximum allowed time to recover failed SCSI devices. This configuration guarantees an I/O response time even when storage hardware becomes unresponsive due to a failure.

9.1. The eh_deadline parameter
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The eh_deadline parameter sets a maximum time limit for SCSI error recovery operations, after which the system resets the entire host bus adapter to prevent indefinite hangs.

The SCSI error handling (EH) mechanism attempts to perform error recovery on failed SCSI devices. The SCSI host object eh_deadline parameter enables you to configure the maximum amount of time for the recovery. After the configured time expires, SCSI EH stops and resets the entire host bus adapter (HBA).

Using eh_deadline can reduce the time:

  • to shut off a failed path,
  • to switch a path, or
  • to disable a RAID slice.
Warning

When eh_deadline expires, SCSI EH resets the HBA, which affects all target paths on that HBA, not only the failing one. If some of the redundant paths are not available for other reasons, I/O errors might occur. Enable eh_deadline only if you have multipath configured on all targets. Also, if your multipath devices are not fully redundant, you should verify that no_path_retry is set large enough to allow paths to recover.

The value of the eh_deadline parameter is specified in seconds. The default setting is off, which disables the time limit and allows all of the error recovery to take place.

Scenarios when eh_deadline is useful

In most scenarios, you do not need to enable eh_deadline. Using eh_deadline can be useful in certain specific scenarios. For example if a link loss occurs between a Fibre Channel (FC) switch and a target port, and the HBA does not receive Registered State Change Notifications (RSCNs). In such a case, I/O requests and error recovery commands all time out rather than encounter an error. Setting eh_deadline in this environment puts an upper limit on the recovery time. That enables the failed I/O to be retried on another available path by DM Multipath.

Under the following conditions, the eh_deadline parameter provides no additional benefit, because the I/O and error recovery commands fail immediately, which enables DM Multipath to retry:

  • If RSCNs are enabled
  • If the HBA does not register the link becoming unavailable

9.2. Setting the eh_deadline parameter
Copia collegamento

Configure the eh_deadline parameter to limit the maximum time allowed for SCSI error recovery. This ensures predictable I/O response times and prevents indefinite hangs, allowing applications to handle unresponsive storage with defined timeout limits.

Procedure

  • You can configure eh_deadline using either of the following methods:

    • defaults section of the multpath.conf file

      From the defaults section of the multpath.conf file, set the eh_deadline parameter to the required number of seconds: 

      # eh_deadline 300
      Copy to Clipboard Toggle word wrap
      Note

      From RHEL 8.4, setting the eh_deadline parameter using the defaults section of the multpath.conf file is the preferred method.

      To turn off the eh_deadline parameter with this method, set eh_deadline to off.

    • sysfs

      Write the number of seconds into the /sys/class/scsi_host/host<host-number>/eh_deadline files. For example, to set the eh_deadline parameter through sysfs on SCSI host 6: 

      # echo 300 > /sys/class/scsi_host/host6/eh_deadline
      Copy to Clipboard Toggle word wrap

      To turn off the eh_deadline parameter with this method, use echo off.

    • Kernel parameter

      Set a default value for all SCSI HBAs using the scsi_mod.eh_deadline kernel parameter. 

      # echo 300 > /sys/module/scsi_mod/parameters/eh_deadline
      Copy to Clipboard Toggle word wrap

      To turn off the eh_deadline parameter with this method, use echo -1.

Legal Notice
Copia collegamento

Copyright © 2025 Red Hat, Inc.
The text of and illustrations in this document are licensed by Red Hat under a Creative Commons Attribution–Share Alike 3.0 Unported license ("CC-BY-SA"). An explanation of CC-BY-SA is available at http://creativecommons.org/licenses/by-sa/3.0/. In accordance with CC-BY-SA, if you distribute this document or an adaptation of it, you must provide the URL for the original version.
Red Hat, as the licensor of this document, waives the right to enforce, and agrees not to assert, Section 4d of CC-BY-SA to the fullest extent permitted by applicable law.
Red Hat, Red Hat Enterprise Linux, the Shadowman logo, the Red Hat logo, JBoss, OpenShift, Fedora, the Infinity logo, and RHCE are trademarks of Red Hat, Inc., registered in the United States and other countries.
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